The present invention relates to a system and method for geolocating a mobile wireless appliance. More particularly, the present invention relates to a system for determining the geographic location of mobile appliances using signals emitted from disparate navigation and/or communications systems.
A geolocation positioning method for determining the geolocation of a mobile appliance capable of receiving reference signals from a plurality of transmitters in disparate communication systems is disclosed. In one embodiment, the method comprises the steps of receiving radio frequency signals at the mobile appliance, identifying reference signals in the received radio frequency signals, determining a time difference of arrival between each pair of identified reference signals, determining a geographic area in which the mobile appliance is located based on the identity of the identified reference signals, and determining a geolocation of the mobile appliance based on the determined time differences of arrival of the identified reference signals by conventional TDOA methods.
One type of prior art geolocation system measures a signal that is emitted by a mobile radio and is received at multiple base stations which are in the same communication network as the mobile radio. The multiple base stations are in separate geographic locations. Each base station conducts time difference of arrival (“TDOA”) measurements of the received signal and the TDOA measurements are used to determine the location the mobile radio using conventional positioning algorithms. A global positioning system (GPS) is typically used to provide a common time reference among the base stations and the mobile radio.
One important attribute of these prior art geolocation systems is that the mobile radio and each of the multiple base stations must all be part of the same communication network so that synchronization can be maintained between the mobile radio and the base stations. Another attribute is that a reverse communication channel must be established between the mobile radio and at least one of the base stations in order for the base stations to make accurate TDOA measurements. Additionally, prior art systems are limited to geolocating a mobile radio only from those base stations in existence at the time the geolocation system is launched. Prior art systems do not have the capability to automatically update, refine, and expand their database of base station locations during a geolocating event.
Attempts have been made to design a mobile radio capable of making TDOA measurements locally at the mobile radio. A system of this design requires that the mobile appliance be capable of receiving GPS signals or timing signals from another time-standard system. However, receiving GPS signals or other time-standard signals at the mobile radio presents special problems. For example, in order for GPS to be effective, the mobile radio must have a clear line of sight to a GPS satellite. This requirement makes the system ineffective in certain areas where direct line of sight is not possible, such as urban environments, wooded and/or mountainous areas, underneath bridges, in tunnels, etc. The slant angles between the GPS satellites and the mobile radio can cause errors due to multipath effects, as well as distortion due to interference from the ionosphere. Additionally, because GPS operates in a different band than the mobile radio, a separate GPS antenna is required in order to receive the GPS signals. The addition of a second antenna makes the mobile radio bulky and cumbersome to carry and use.
For other time-standard signals, the communication network must be modified so as to send the time-standard signals to the mobile appliance. Such a modification to the communication network may be prohibitively expensive and therefore impractical.
Another type of prior art geolocation system measures the direction from which a mobile radio signal is received. A mobile radio transmits a signal which is received by multiple base stations in separate geographic locations. Each base station has an antenna array which measures the radio wave phase difference at different antenna elements in the array. An angle of arrival of the mobile radio's signal is calculated and a line of bearing to the mobile radio is determined. The intersection of the lines of bearing from the multiple base stations determine the geolocation of the mobile radio.
Geolocation systems that measure the angle of arrival are susceptible to error due to multipath signals arriving at the antenna arrays from different directions. Additionally, the base stations require an antenna array, rather than a single antenna, in order to determine the angle of arrival of the mobile radio's signal. The need for the addition of an antenna array at the base stations presents a significant cost issue.
Yet another type of prior art geolocation system uses a time ranging technique which measures the time required for a signal which is emitted from a base station to be received by the mobile radio. The time required for the mobile radio to receive a base station's signal defines a circular locus of location points around the base station. The intersection of the circular locus of location points from multiple base stations determines the geolocation of the mobile radio.
The time ranging technique requires that the mobile radio and each of the multiple base stations must all be part of the same communication network so that synchronization can be maintained between the mobile radio and the base stations. If the mobile radio entity calculating location does not know exactly when the base station emitted the ranging signal, the locus of location points around the base station cannot be determined. Additionally, a reverse communication channel must be established between at least one of the base stations and the mobile radio, in order to determine the intersection of the circular locus of location points from the multiple base stations.
Thus, there is a need for a geolocation system in which the geolocation of mobile appliances can be determined without requiring the mobile appliance to be in communication with multiple base stations in the same communication network as the mobile appliance. There is also a need for a compact mobile appliance which does not need to be synchronized with a particular communication network in order for the mobile appliance to be geolocated. Additionally, the measurement of timing signals at the mobile appliance without the need to receive input from any fixed network is desirable.
These and other needs are satisfied by the geolocation positioning system and method of the present invention which is configured to determine the geolocation of a mobile appliance capable of receiving reference signals from a plurality of reference signal transmitters in disparate navigation or communication systems. Under one embodiment of the present invention, the reference signal transmitters need not be synchronized with the mobile appliance in order to geolocate the mobile appliance. Furthermore, the mobile appliance receives reference signals and makes timing measurements without assistance from any fixed network; no forward link data needs to be sent to the mobile appliance from a fixed network.
The mobile appliance can be any one or more of the following: laptop computer, mobile telephone, mobile radio, walkie-talkie, personal digital assistance, pager, personal tracking device, vehicle, automotive anti-theft device, telemetry device, fleet tracking device, anti-location fraud device, or any other similar device or system for which the geolocation of the device or system is desired.
The reference signals can be, for example, one or more of the following: J-STD 008/IS-95 pilot signals, mobile telephone timing signals, wireless communications network timing signals including 3G air interface networks, GPS differential correction timing signals, or GPS/GNSS augmentation signals. It is to be understood that the invention is not limited to only those systems that use the above-mentioned signals, rather the invention can be used with any reference signal that is linked to a time standard and used by a communication and/or navigation system typically to synchronize various base stations, emitters, mobile appliances, users of the system, etc. It is to be appreciated that other signals that are inherent in a communications system may also be used as a reference signal by the present inventive system and method. As used herein, reference signals, timing signals, pilot signals, and psuedolites all relate to one or more of the above-mentioned signals.
The benefits of using the present inventive system and method are many and varied, such as locating a mobile appliance for safety reasons, to effect a rescue, for vehicle or personal tracking, for location specific billing, and other like functions that would be apparent to those of skill in the art.
Accordingly, it is an object of the present invention to provide a novel system and method of geolocating a mobile appliance from a plurality of reference signal sources in disparate navigation and/or communication systems.
It is another object of the present invention to provide a novel system and method of geolocating a mobile appliance from a plurality of reference signal sources in the same communication system.
It is yet another object of the present invention to provide a novel system and method for geolocating a mobile appliance from the differences in the times of arrival of reference signals received by the mobile appliance without the need to receive synchronization signals from the fixed network.
It is still another object of the present invention to provide a novel system and method of geolocating a mobile appliance from a plurality of reference signal sources wherein the mobile appliance is not synchronized with any of the plurality of reference signal sources.
It is a further object of the present invention to provide a novel system and method of updating a database of geolocation information for a plurality of reference signal sources and automatically updating the geolocation information in the database with data obtained from geolocation events.
It is yet a further object of the present invention to provide a novel system and method of adding the geolocation information and the reference signal code phases and frequencies for a new reference signal source to the database of reference signal sources and automatically updating the geolocation information in the database with data obtained from geolocation events.
It is still a further object of the present invention to provide a novel system and method for geolocating a mobile appliance for safety reasons, to effect a rescue, for vehicle or personal tracking, or for location specific billing.
It is still a further object of the present invention to provide a novel system and method for geolocating a mobile appliance by a two step process.
It is still a further object of the present invention to provide a novel system and method for geolocating a mobile appliance by transmitting signals from the mobile appliance to a fixed network where the signals transmitted are representative of the difference in the time of arrival at the mobile applicant of the signals from the reference signal sources in disparate communication systems.
It is still a further object of the present invention to provide a novel system and method for geolocating a mobile appliance which includes a geolocation station that is entirely passive.
It is still a further object of the present invention to provide a novel system and method for geolocating a mobile appliance which includes a geolocation station that is not in communication with the reference signal sources.
It is still a further object of the present invention to provide a novel system and method for geolocating a mobile appliance which includes a geolocation station that does not transmit a signal to the mobile appliance.
It is still a further object of the present invention to provide a novel system and method for geolocating a mobile appliance where the mobile appliance stores the received reference signals in a buffer before conducting signal detection and measurement.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.